Aggregatibacter actinomycetemcomitans is an oral pathogen associated with aggressive periodontitis, oral abscesses, and proliferation of osteoclasts leading to bone loss. Epidemiological evidence suggests that the presence of cytolethal distending toxin (CDT) genes is associated with aggressive periodontitis. CDTs are thought to function in vivo by blocking cellular division and/or directly killing epithelial and immune cels. Despite the fact that a large number of important human pathogens produce CDTs, the mechanism by which this family of toxins interacts with host cells is currently understudied. This application proposes a non-biased somatic cell genetic approach to identify host factors that confer sensitivity to CDT from A. actinomycetemcomitans. CDT resistant mutant cels will be investigated with biochemical methods and fluorescent microscopy colocalization assays to characterize what step in the CDT intoxication pathway is deficient. Further, a cDNA expression library will be used to identify host genes that are necessary for CDT intoxication. Identification of the host genes involved with CDT intoxication and characterization of the CDT intoxication pathway will inform future studies on therapeutic intervention of A. actinomycetemcomitans infection. PUBLIC HEALTH RELEVANCE: Aggregatibacter actinomycetemcomitans is an oral pathogen associated with aggressive periodontitis, oral abscesses, osteoclastogenesis and several extra-oral pathologies such as endocarditis, meningitis, and osteomyelitis. Epidemiological studies have shown that strains of A. actinomycetemcomitans that encode a recently discovered toxin, cytolethal distending toxin (CDT), are significantly associated with aggressive periodontitis. Although many studies have shown that CDT is an important virulence factor, little is known about how CDTs intoxicate host cells; therefore, we propose to identify and characterize the host factors that are required for sensitivity to CDT in order to better understand the mechanism of intoxication and inform future studies on therapeutic toxin inhibitors.